I'm looking at a scan of the 1900 United States census right now. Column 19 says "Occupation". The particular individual I'm looking at has the word "stonemason" written in that box. The next column says "Months not employed". In the box of the individual of interest, there is the number "4". Does that mean he was unemployed four months every year, he has been unemployed the last four months, he is unemployed every April, or something else?
Here is a link to the census so you can see it.
1900 Census: Instructions to Enumerators
221. Column 20. Months not employed.—The object of this question is to get the number of months (or parts of months) in the census year (June 1, 1899, to May 31, 1900) during which each person having a gainful occupation was not employed. for those who have no gainful occupation, leave the column blank.
222. The law does not contemplate that this question shall apply solely to the principal occupation in which the person may have been engaged during the year, but it is the intent to find out the number of months (or parts of months) during which a person ordinarily engaged in gainful labor was not employed at all.
In other words, if the question was answered accurately he was unemployed for 4 months out of the past twelve (Jun 1889 to May 1900).
The instructions to the enumerator for column 20 said:
The object of this question is to get the number of months (or parts of months) in the census year (June 1, 1899, to May 31, 1900) during which each person having a gainful occupation was not employed.
So the "4" means the subject happened to have been unemployed for four of the last twelve months.
One can often find instructions or descriptions for census columns online, such as this IPUMS page for the 1900 census.
